ULN2803 Implementation Question

[chrisaxeman]

Hi Guys,

It's been a long time!

Question I have concerns using a ULN2308 to drive some relays. The input trigger voltage for the ULN2308 will be relay driven. Do I need anything like some type of de-bounce circuitry before or after the ULN2308?

I'm building an active breakout box prototype. It is to be used with an RJM Amp Gizmo half-rack function switcher.

The RJM has eight function relays. These are controlled by MIDI messages. The idea of the breakout box is to be able to separate the ground connections from the relays. In their current configuration, mixing the grounds to some degree between relays is unavoidable.

RJM used to offer an active breakout box called the BOB-8 that isolated the 8 relays from one another fully. I thought I'd have a go at making my own.

Type of circuits I was looking at were like some of these:

https://i.stack.imgur.com/Pqto2.png

https://www.twovolt.com/2016/08/24/8-channel-relay-driver-using-uln2803-sugar-cube-relay/

Any help would be appreciated before I get too deep in (I've drilled the box already, so maybe I am).

Another thought I had was something Arduino to give it exclusive control over MIDI, but I'm happy to get this break out box working first, with Arduino being a bit beyond my capability.

Cheers

Chris.

[Sweetalk]

I think that any of those circuits will work as you need. The shared ground is on the coil side, not in the switch, so the signal ground will be isolated from each other.

As for the debouce I don't think you'll need any. Wich relay you'll use?

[chrisaxeman]

I think that any of those circuits will work as you need. The shared ground is on the coil side, not in the switch, so the signal ground will be isolated from each other.

As for the debouce I don't think you'll need any. Wich relay you'll use?

Thanks Sweetalk.

Have a bunch of little Fujitsu FBR211 signal relays https://www.fcl.fujitsu.com/downloads/MICRO/fcai/relays/fbr211.pdf

It's all function switching for amps. So not really audio, but part of a bigger picture where I'm trying to avoid ground loops.

Most of the time I could get away with the 4 x TRS setup on the RJM unit as it is. Though as the setup is rack mounted, the breakout box will be mounted in the rear of the rack as an interface. To be able to use it with any of my amps easily is the hope.

Cheers

Chris.

[chrisaxeman]

Hi Guys,

Took me a while through this with Covid in November than the Christmas/NY rush but came up with this one. Could/Should have come up with a more efficient design with less PTP and flying leads (hard to get the lid on lol, especially ultimately sending wiring away from both poles of the relays just in case I had to flip polarity - didn't need to with the RJM). But was trying to save money using up parts I had. But was hard to make.

The 4 jacks labelled 1/2 etc. are for TRS, unless the companion jack to the right (say jack 2) is plugged into, then they each become separately isolated jacks. Say my Mesa Mkiii for instance, uses TS for Clean/lead and R2 mode, but TRS for EQ and Reverb. So opens the option up to not needing breakout cables depending on the application.

On the other side, there is an 8-pin DIN socket isolated from the enclosure with an O-ring super glued to the metal face and mounted with plastic bolts. The relays from the RJM return through the Din Plug body, so it needs to be kept above ground. The DC jacks are obviously the same, and used the plastic bolts again the mount those, and also to secure the PCB.  The DC feed throughs are just in parallel, but they are destined to power the RJM and an Axess CFX4 function switcher. They are all isolated from ground so this shouldn't be a problem in the rig. Will be supplied by a 650ma 9vdc tap all up.

There a 7805 and all of the resisitors for the low-side switching circuit. I PTPed that bit on the outside of the box with the jacsk and just flipped it over to mount it all inside.

PCB was my first shot at double-sided and was painful. Got lucky with the alignment but needed a lot of repairs as I went. Tried to squeeze a lot on there, including the LED dropping resistors, pins and flying leads etc. Had to engineer in connections in places where I could solder between sides, as I don't have a clue how to do plated through holes. Used some left over press'n'peel off a drawing I did in PCB123. Box layout and text was on Front Panel Designer, Labels clear shipping from a laser printer.

Works well after all that

[ElectricDruid]

Cripes, have you never heard of ribbon cables?!?  Or maybe just thinner wire?

Good work though, if you've got it all in there and working. That's ultimately what counts. Especially with a DIY double-sided board. If I need double -sided, I do gerbers and get them made, I have to say. I bottled out trying to do that myself, so fair play.

Tom

[chrisaxeman]

Cripes, have you never heard of ribbon cables?!?  Or maybe just thinner wire?

Good work though, if you've got it all in there and working. That's ultimately what counts. Especially with a DIY double-sided board. If I need double -sided, I do gerbers and get them made, I have to say. I bottled out trying to do that myself, so fair play.

Tom

Lol.....thanks (I think).

The physical format in the rack it is going into is perfect. It is a proto, but it works. 

Wire was only 0.4mm square btw. Might be the photos making it look bigger!  Ribbon cable is a bit hard to get connected to 1/4" jacks and chassis mount LEDs - wouldn't gain anything there.

If I do another one in that physical format, I'd do it all PCB mount, using the lid to drop it in, and fix the DC jacks and DIN socket on the other side with screws.

As for fitting in? I've worked as an electrical technician in underground coal mining for 34 years. Somehow getting things to fit into spaces they're not supposed to (and maintaining them) is normal for me.

Cheers.

[ElectricDruid]

Wire was only 0.4mm square btw. Might be the photos making it look bigger!  Ribbon cable is a bit hard to get connected to 1/4" jacks and chassis mount LEDs - wouldn't gain anything there.

Yeah, it looks fatter than that in the pics, for sure.

If I do another one in that physical format, I'd do it all PCB mount, using the lid to drop it in, and fix the DC jacks and DIN socket on the other side with screws.

That would have been my approach, PCB mount everything possible, probably on two boards, and then join the two boards with ribbon cable or a connector of some kind. I guess I just hate wiring. Everyone seems to do it wrong too, me included. It's much harder to miswire something board-mounted!

As for fitting in? I've worked as an electrical technician in underground coal mining for 34 years. Somehow getting things to fit into spaces they're not supposed to (and maintaining them) is normal for me.

Those are handy skills to have!

Nice work, again.

BTW, you can put a "width" attribute in your image tags to make the photos display at a smaller size, like this:

[img width=800]https://url_of_some_image.jpg[/img]

[chrisaxeman]

Wire was only 0.4mm square btw. Might be the photos making it look bigger!  Ribbon cable is a bit hard to get connected to 1/4" jacks and chassis mount LEDs - wouldn't gain anything there.

Yeah, it looks fatter than that in the pics, for sure.

If I do another one in that physical format, I'd do it all PCB mount, using the lid to drop it in, and fix the DC jacks and DIN socket on the other side with screws.

That would have been my approach, PCB mount everything possible, probably on two boards, and then join the two boards with ribbon cable or a connector of some kind. I guess I just hate wiring. Everyone seems to do it wrong too, me included. It's much harder to miswire something board-mounted!

As for fitting in? I've worked as an electrical technician in underground coal mining for 34 years. Somehow getting things to fit into spaces they're not supposed to (and maintaining them) is normal for me.

Those are handy skills to have!

Nice work, again.

BTW, you can put a "width" attribute in your image tags to make the photos display at a smaller size, like this:

[img width=800]https://url_of_some_image.jpg[/img]

Thanks mate. I cut the pics down. Used to my other forums automatically cutting the image size down, as I link straight from Imgur.

I certainly need to simplify my construction techniques, but parts have gotten so expensive in the last 2-3 years, I'm trying to use up what I have.

Had all of those parts on hand. Hate those IP65 rated boxes - always removing lumps and bumps with a Dremel. But got them out of the plastic bag after 15 years!

Cheers for the encouragement, ED.

Chris.